Pop up the mattress plug and open the cap. Do not lift up on the plug after removing the cap, as this can cause more air to be inserted into the mattress.
Lay the broom handle across the length of the bed, slowly push any air pockets towards the plug and force the air through the valve. Make sure the room is brightly lit during this process so you can see the bubbles through the mattress and ensure that you have removed them all. Keep a towel handy to mop up any water that escapes from the plug.
Pour waterbed conditioner into the mattress to prevent air bubbles from forming in the future.
Replace the cap and push the plug back into the mattress. Repeat periodically as needed.